Scene
Ground
Ramp (wood)
Wall (brick)
Crate
Forces
Weight (mg)
Normal (N)
Applied (F)
Friction (f)
mg components
Velocity (v)
Acceleration (a)
Graphs
Position s
Velocity v
Acceleration a
Net Force ΣF
Ramp: Forces & Motion
Push a block along flat ground toward an inclined ramp. Does it reach the wall at the top? Explore how angle, mass, friction, and applied force determine the outcome.
Topics
Force
How forces combine on an incline — gravity decomposition, normal force, friction.
Position
Where the block is along the path — ground vs ramp vs wall.
Velocity
How fast and in which direction — sign tells uphill vs downhill.
Acceleration
Rate of velocity change — directly proportional to net force (Newton’s 2nd law).
Sample Learning Goals
- Predict, qualitatively, how an external force will affect the speed and direction of an object’s motion.
- Explain the effects with the help of a free body diagram.
- Use free body diagrams to draw position, velocity, acceleration and force graphs — and vice versa.
- Explain how the graphs relate to one another.
- Given a scenario or a graph, sketch all four graphs.
The Experiment
The block starts on flat ground. Apply a horizontal force to accelerate it. When it reaches the ramp base, its momentum carries it uphill — but gravity and friction fight back. Adjust parameters to find the minimum force needed to reach the wall.
Force Decomposition
On the ramp, the horizontal applied force and gravity both decompose into components along and perpendicular to the surface:
- Gravity along ramp:
mg sin θ — pulls the block downhill
- Gravity into surface:
mg cos θ — contributes to normal force
- Applied along ramp:
F cos θ — pushes uphill
- Applied into surface:
F sin θ — increases normal force (and friction!)
Normal force: N = mg cos θ + F sin θ
Toggle "mg Decomposition" to see the light-blue decomposition arrows in 3D.
Friction: Static vs Kinetic
- Static friction adjusts to prevent motion:
|fs| ≤ μs · N. The readout shows what % of max static friction is used.
- Kinetic friction acts once sliding:
fk = μk · N. Since μk < μs, once it starts moving, less force is needed to keep it going.
Critical Angle: θc = arctan(μs)
The steepest angle at which the block stays still (no applied force). With μs=0.5, this is arctan(0.5) ≈ 26.6°. Try the "Critical θ" preset.
How the Graphs Relate
- Force → Acceleration:
a = ΣF / m — the acceleration graph is just the force graph divided by mass. They have the same shape.
- Acceleration → Velocity: Acceleration is the slope of velocity. Constant acceleration → velocity is a straight line.
- Velocity → Position: Velocity is the slope of position. Constant velocity → position is a straight line. Changing velocity → position is a curve.
- When ΣF = 0: Acceleration = 0, velocity is constant, position changes linearly (or stays still if v = 0).
Try These Experiments
- Minimum force to reach the wall: Set angle=30°, μk=0.3. What’s the smallest applied force that gets the block to the wall? Watch the Time graph to see v go to zero just as it arrives.
- Frictionless slide: “Frictionless” preset. On the ramp,
a = g sin θ. At 30°, that’s ≈ 4.9 m/s². Verify on the graph.
- Mass doesn’t matter: Frictionless ramp, change mass 1–50 kg. Acceleration stays the same! (Mass cancels in
a = g sin θ.)
- Read the graphs: Apply force 50N, switch to Time tab. When the block is on flat ground, the acceleration graph is constant. When it hits the ramp, acceleration drops (gravity opposes). When it stops, acceleration may flip sign. Sketch what you expect first, then check.
- Energy conservation: Switch to Energy tab. Without friction: KE + PE = constant (green line is flat). With friction: total energy decreases — the gap is heat from friction.